As is known, a filter comprises an external casing, generally formed by a beaker-shaped body and a relative closing cover, which is provided with an inlet conduit for a fluid to filter and an outlet conduit for the filtered fluid, and a filter cartridge designed to sub-divide the internal volume of the casing into at least two distinct chambers, of which a first chamber communicating with the inlet conduit and a second chamber communicating with the outlet conduit. A typical filter cartridge comprises a support plate to which is fixed an end of a tubular filter wall, for example a pleated filter wall having a star-shaped geometry or a depth wall, the other end of which is fixed to a second support plate.
One of the support plates is destined to close the internal cavity of the filter wall, while the opposite plate exhibits, in general terms, an opening destined to place the internal cavity in communication with the inlet conduit or alternatively the outlet conduit of the filter.
Further, one of the support plates can sometimes be conformed such as to house a perimeter seal, which is destined to be interposed between the closing cover and the beaker-shaped body of the filter casing such as to hermetically close it.
It is further possible for the cartridge to exhibit a secondary filter wall located downstream of the first filter wall with reference to the flow direction of the fuel from the inlet conduit to the outlet conduit.
Generally the secondary filter wall is also a star-shaped pleated filter wall or a depth wall which is coaxially associated to the first filter wall.
The second filter wall generally exhibits a larger porosity than the first filter wall, as in normal use it is mainly tasked with separating the water which can be present in the filtered fluid by coalescence.
The water which separates from the filtered fluid generally collects on the bottom of the external casing of the filter, where special discharge means are present.
The filters of known type can further comprise a by-pass conduit, provided with a respective valve, which is destined to by-pass the first filter wall when it is clogged.
In this way, a certain quantity of fluid is guaranteed to exit from the filter and it is also sure to be without the larger-dimension impurities as it will pass through the secondary filter wall.
Various consumer components are present in the filter, among which, in particular, components subject to wear, such as the above-mentioned seal, and components subject to progressive clogging, such as the filter walls.
The consumer components consequently require periodical maintenance interventions for substitution thereof, as they progressively become worn or blocked up.
In an attempt to reduce the number of maintenance interventions, the secondary filter wall has been so dimensioned as to make its working life of the same length as the whole filter, i.e. so that the secondary filter wall does not by itself require replacing during the life of the whole filter.
However, in order to achieve this, it is necessary to make the secondary filter wall such that it exhibits a passage surface which is sufficient not to clog over its working life.
Therefore, the secondary filter wall exhibits considerable spatial dimensions internally of the filter casing, and leads to the need to design casings having a conformation and design which are appropriate for the presence of the secondary filter wall.
A further drawback of known filters is having to predispose discharge means of the water on the bottom of the external casing of the filter. This location leads to a greater constructional complication of the beaker body which defines the bottom of the external casing, and further leads to some limitations regarding the installation of the filter. The filter has always to be installed in a sufficiently large space not only for enabling connection of the inlet and outlet conduits of the fluid to be filtered, which are positioned at the upper cover, but also for guaranteeing accessibility of the water discharge means, which are at the bottom of the beaker body.